1. Field of the Invention
The present invention relates to replaceable gage pads for rotary-type earth boring drill bits. Particularly, the present invention relates to gage pads that may be removably secured to a rotary-type drill bit. The present invention also relates to modular drill bits which include a bit body and one or more replaceable gage pads securable thereto. Methods of testing different types of gage pads, methods of replacing the gage pads of a drill bit, and methods of altering the balance or net imbalance of a drill bit are also within the scope of the present invention.
2. Background of the Related Art
Conventional rotary-type earth boring drill bits, including drag bits, roller-cone bits, and other drill bits, typically include fixed, integral gage pads or other bearing surfaces that maintain the gage of the bore hole being drilled and prevent whirl and vibration of the drill during drilling.
The cutters of state of the art earth boring drill bits typically resist wear and, thus, may outlast other bit components, such as the gage pads and other bearing surfaces of the drill bit. Thus, while the cutters of a drill bit may continue to effectively drill through a formation, the gage pads may be worn, which may result in vibration of the drill bit during drilling and, therefore, a non-circular bore hole, or well. If the cutters at the gage also become worn, an undergage bore hole, or a bore hole with a smaller diameter than that of a new drill bit employed therein, may result. Reaming of an undergage borehole is typically required to bring the bore hole to full gage, or diameter. Reaming is, however, somewhat undesirable since it necessitates additional drilling time and expense. An undergage bore hole may also damage a new bit during insertion of same into the bore hole. An undergage bore hole may also cause the casing or the drill string to become stuck in the bore hole, necessitating expensive and time consuming remedial operations or the abandonment of expensive drilling equipment.
Thus, when a drill bit is no longer able to drill a full gage bore hole, the useful life of the drill bit has ended, even if the expensive cutters and other components thereof are still useful.
Similarly, in order to test a new type of gage pad, a gage pad with a particular type of surface, a particular gage pad configuration, or a gage pad that includes new features or components, it is typically necessary to fabricate a separate prototype drill bit for each variation in the tested gage pads. Thus, the testing of different types of gage pads may be very costly, and a large amount of time may be required to fabricate each prototype drill bit.
Moreover, although the tested gage pads of the prototype drill bit may not be useful for their intended purpose, or may otherwise be undesirable, the other components of the prototype drill bit may still have a long, useful life. Nevertheless, the prototype drill bit, along with many of the components thereof, would have to be scrapped. Thus, the drill bit and many of its components, as well as the time required to fabricate the drill bit, are wasted.
A typical bore hole may pass through several types of rock formations. Since different types of earth boring drill bits are designed to drill through only one or a few specific types of formations, more than one type of drill bit may be required to drill the bore hole. As the types of formations that will be encountered as a bore hole is drilled may not be known prior to actually drilling the bore hole, however, the types of drill bits that will be required may also not be known. Accordingly, either several types of drill bits must be on hand at the drilling site, or the drilling operation may cease until the appropriate type of drill bit is delivered to the drilling site.
It may also be desirable to alter the mass balance or net mass imbalance (i.e., the center of gravity) of a drill bit so as to eliminate, reduce, or otherwise counteract unexpected vibration, or "whirl" or cutter force imbalance, that may be encountered during drilling. However, the balance or net imbalance of typical conventional earth boring drill bits may not be altered.
Accordingly, an earth boring drill bit with modular, removeable gage pads is needed to improve the useful life of earth boring drill bits, to reduce or eliminate unwanted vibration of the drill bit during drilling, to facilitate customization of the drill bit at the drilling site, and to reduce testing and drilling costs.